[Python-checkins] gh-88831: In docs for asyncio.create_task, explain why strong references to tasks are needed (GH-93258)
ambv
webhook-mailer at python.org
Tue Jun 7 04:56:14 EDT 2022
https://github.com/python/cpython/commit/75ceae05c11461beda65e6170b67b0b42fd55cd0
commit: 75ceae05c11461beda65e6170b67b0b42fd55cd0
branch: main
author: Andreas Grommek <76997441+agrommek at users.noreply.github.com>
committer: ambv <lukasz at langa.pl>
date: 2022-06-07T10:56:09+02:00
summary:
gh-88831: In docs for asyncio.create_task, explain why strong references to tasks are needed (GH-93258)
Co-authored-by: Łukasz Langa <lukasz at langa.pl>
files:
A Misc/NEWS.d/next/Documentation/2022-05-26-14-51-25.gh-issue-88831.5Cccr5.rst
M Doc/library/asyncio-task.rst
diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst
index 8e3d49dcf9d71..7796e47d4674d 100644
--- a/Doc/library/asyncio-task.rst
+++ b/Doc/library/asyncio-task.rst
@@ -226,7 +226,24 @@ Creating Tasks
.. important::
Save a reference to the result of this function, to avoid
- a task disappearing mid execution.
+ a task disappearing mid execution. The event loop only keeps
+ weak references to tasks. A task that isn't referenced elsewhere
+ may get garbage-collected at any time, even before it's done.
+ For reliable "fire-and-forget" background tasks, gather them in
+ a collection::
+
+ background_tasks = set()
+
+ for i in range(10):
+ task = asyncio.create_task(some_coro(param=i))
+
+ # Add task to the set. This creates a strong reference.
+ background_tasks.add(task)
+
+ # To prevent keeping references to finished tasks forever,
+ # make each task remove its own reference from the set after
+ # completion:
+ task.add_done_callback(background_tasks.discard)
.. versionadded:: 3.7
diff --git a/Misc/NEWS.d/next/Documentation/2022-05-26-14-51-25.gh-issue-88831.5Cccr5.rst b/Misc/NEWS.d/next/Documentation/2022-05-26-14-51-25.gh-issue-88831.5Cccr5.rst
new file mode 100644
index 0000000000000..983bea981a9b2
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2022-05-26-14-51-25.gh-issue-88831.5Cccr5.rst
@@ -0,0 +1 @@
+Augmented documentation of asyncio.create_task(). Clarified the need to keep strong references to tasks and added a code snippet detailing how to to this.
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